Photoprotective Activity of Lichen Extracts and Isolated Compounds in Parmotrema Tinctorum

Abstract

Lichens are an excellent source for the discovery and development of new photoprotective compounds. However, investigation on their bioactivities remains limited, especially in Vietnam. In this study, six lichen extracts (Parmotrema poolii, P. sancti-angelii, P. tinctorum, Usnea baileyi, U. pulvinulata, U. undulata) and five isolated compounds from commonly distributed species P. tinctorum (methyl β-orcinol carboxylate (1), atranorin (2), lecanorol (3), salazinic acid (4), 1β-acetoxyhopan-3β,22-diol (5)) have been screened in vitro for their photoprotective activity. The photoprotective potential was investigated by determination of their absolute (UV-PF, c, UVA-PF) and relative indexes (SUI, ISP). The structures of isolated compounds were elucidated by spectroscopic methods and confirmed by X-ray diffraction. The results showed that P. poolii, P. sancti-angelii, P. tinctorum, U. baileyi, U. undulata, and compounds of methyl β-orcinol carboxylate (1) and salazinic acid (4) acted as strict UVB filters, and their photoprotective activities are comparable to that of the commercial UVB filter (4-methylbenzylidene camphor). Meanwhile, U. pulvinulata acted as a UVA booster. Compound (3) presented characteristics of a UVA filter, (2) protected well from both UVA and UVB while (5) exhibited a weak photoprotective activity. For the first time, this work successfully extracted several highly potential solar photoprotective compounds from Vietnam's lichens.